Question

A 65.7 g sample of an element contains 4.95×10²³ atoms. Identify the element?

Answer 1

The element is bromine.

Step 1. Calculate the number of moles of the element.

`n = 4.95 × 10^23" atoms" × ( 1"mol")/(6.022 × 10^23"atoms")` = 0.8220 mol

Step 2. Calculate its molar mass.

Molar mass = `(65.7"g")/(0.8220"mol")` = 79.9 g/mol

Step 3. Identify the element.

Look in the Periodic Table for an element with atomic mass 79.9 u. It's bromine!